From 4654b690fe7e0d7bcf170f8200ddb00b14223dca Mon Sep 17 00:00:00 2001
From: Andrea Cavalli <andrea@cavallium.it>
Date: Wed, 29 Nov 2023 15:49:09 +0100
Subject: [PATCH] Improve immutable wrapped array list performance

---
 .../plugin/classgen/GenSerializerArrayX.java    |  4 ++--
 .../nativedata/ImmutableWrappedArrayList.java   | 17 +++++++++++++++--
 .../datagen/nativedata/UpgradeUtil.java         |  2 +-
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/datagen-plugin/src/main/java/it/cavallium/datagen/plugin/classgen/GenSerializerArrayX.java b/datagen-plugin/src/main/java/it/cavallium/datagen/plugin/classgen/GenSerializerArrayX.java
index bc168cc..d0f60f0 100644
--- a/datagen-plugin/src/main/java/it/cavallium/datagen/plugin/classgen/GenSerializerArrayX.java
+++ b/datagen-plugin/src/main/java/it/cavallium/datagen/plugin/classgen/GenSerializerArrayX.java
@@ -125,9 +125,9 @@ public class GenSerializerArrayX extends ClassGenerator {
 
 		method.addCode("\n");
 		if (USE_NATIVE_TYPED_ARRAYS) {
-			method.addStatement("return new $T(a)", ParameterizedTypeName.get(ClassName.get(ImmutableWrappedArrayList.class), arrayComponentTypeName));
+			method.addStatement("return $T.of(a)", ParameterizedTypeName.get(ClassName.get(ImmutableWrappedArrayList.class), arrayComponentTypeName));
 		} else {
-			method.addStatement("return ($T) new $T(a)",
+			method.addStatement("return ($T) $T.of(a)",
 					ParameterizedTypeName.get(ClassName.get(ImmutableWrappedArrayList.class), arrayComponentTypeName),
 					ClassName.get(ImmutableWrappedArrayList.class)
 			);
diff --git a/datagen/src/main/java/it/cavallium/datagen/nativedata/ImmutableWrappedArrayList.java b/datagen/src/main/java/it/cavallium/datagen/nativedata/ImmutableWrappedArrayList.java
index 71bd3ab..bbe4963 100644
--- a/datagen/src/main/java/it/cavallium/datagen/nativedata/ImmutableWrappedArrayList.java
+++ b/datagen/src/main/java/it/cavallium/datagen/nativedata/ImmutableWrappedArrayList.java
@@ -32,6 +32,8 @@ import java.util.function.Consumer;
 import org.jetbrains.annotations.NotNull;
 
 public class ImmutableWrappedArrayList<K> extends AbstractObjectList<K> implements RandomAccess {
+
+	private static final ImmutableWrappedArrayList<?> EMPTY = new ImmutableWrappedArrayList<>(new Object[0]);
 	/** The backing array. */
 	protected final K[] a;
 	/** The current actual size of the list (never greater than the backing-array length). */
@@ -42,7 +44,7 @@ public class ImmutableWrappedArrayList<K> extends AbstractObjectList<K> implemen
 	 *
 	 * @param a an array whose elements will be used to fill the array list.
 	 */
-	public ImmutableWrappedArrayList(final K[] a) {
+	private ImmutableWrappedArrayList(final K[] a) {
 		this.a = a;
 		this.size = a.length;
 	}
@@ -55,7 +57,18 @@ public class ImmutableWrappedArrayList<K> extends AbstractObjectList<K> implemen
 	 */
 	@SafeVarargs
 	public static <K> ImmutableWrappedArrayList<K> of(final K... init) {
-		return new ImmutableWrappedArrayList<>(init);
+		return init.length == 0 ?  of() : new ImmutableWrappedArrayList<>(init);
+	}
+
+	/**
+	 * Creates an array list using an array of elements.
+	 *
+	 * @param init a the array the will become the new backing array of the array list.
+	 * @return a new array list backed by the given array.
+	 */
+	public static <K> ImmutableWrappedArrayList<K> of() {
+		//noinspection unchecked
+		return (ImmutableWrappedArrayList<K>) EMPTY;
 	}
 
 	private UnsupportedOperationException ex() {
diff --git a/datagen/src/main/java/it/cavallium/datagen/nativedata/UpgradeUtil.java b/datagen/src/main/java/it/cavallium/datagen/nativedata/UpgradeUtil.java
index ef00f5d..5e48ea8 100644
--- a/datagen/src/main/java/it/cavallium/datagen/nativedata/UpgradeUtil.java
+++ b/datagen/src/main/java/it/cavallium/datagen/nativedata/UpgradeUtil.java
@@ -16,7 +16,7 @@ public class UpgradeUtil {
 		for (int i = 0; i < array.length; i++) {
 			array[i] = (B) upgrader.upgrade((A) array[i]);
 		}
-		return (ImmutableWrappedArrayList<B>) new ImmutableWrappedArrayList<>(array);
+		return (ImmutableWrappedArrayList<B>) ImmutableWrappedArrayList.of(array);
 	}
 
 	public static <A, B> B upgradeNullable(A nullableValue, DataUpgrader<A, B> upgrader) {